As an apparatus configured to drive a rotary machine such as a compressor, there is an apparatus including an electric driving device configured to generate a rotational driving force and a transmission device configured to change the speed of the rotational driving force generated by the electric driving device and then transmit the speed-changed rotational driving force to the rotary machine.
Patent Document 1 discloses an apparatus including: a constant-speed motor and a variable-speed motor for speed change as an electric driving device; and a planetary gear transmission device as a transmission device. The apparatus makes it possible to change the rotation rate of the variable-speed motor to change the rotation rate of the output shaft of the transmission device connected to a rotary machine.